The evolution of light-weight, easily erected and economical portable shelters has led to the increasing commercial and private use of these structures. Portable shelters typically employ a cloth or plastic material attached to a light-weight, highly foldable skeleton or frame structure. The cloth provides a roof and/or walls for the shelter, and the frame structure provides support for the cloth, for example, the frame structure includes legs to elevate the roof and a system of trusses to support the roof and to generally stabilize the shelter. The frame structure often incorporates a compound, scissor-like, arrangement of a light-weight, tubular material such as aluminum. In order to maximize the usable area under a shelter, the frame structure is often designed so that the roof is supported solely by legs positioned near the perimeter of the roof. Stated alternatively, shelters do not typically employ an interior supporting post or leg such as a leg or post positioned in the center of shelter. U.S. Pat. No. 4,641,676 to Lynch and U.S. Pat. No. 7,367,348 to Tsai et al., the contents of which are herein incorporated by reference, are examples of such portable shelters.
Unfortunately, the design objectives of internally unsupported roofs and light-weight and foldable frame structures, often results in portable shelters that are unstable in wind and that suffer from sagging or collapsing roofs and peaks. What is needed in the art is a frame structure for a portable shelter that provides increased stability and prevents sagging and collapsing while maintaining the design objectives of maximizing usable space, foldability, and light-weight.